Generally, memory used to store data in a computing system can be volatile (to store volatile information) or non-volatile (to store persistent information). Volatile data structures stored in volatile memory are generally used for temporary or intermediate information that is required to support the functionality of a program during the run-time of the program. On the other hand, persistent data structures stored in non-volatile memory are available beyond the run-time of a program and can be reused. Moreover, new data is typically generated as volatile data first, before the user or programmer decides to make the data persistent. For example, programmers or users may cause mapping (i.e., instantiating) of volatile structures in volatile main memory that is directly accessible by a processor. Persistent data structures, on the other hand, are instantiated on non-volatile storage devices like rotating disks attached to Input/Output (I/O or IO) buses or non-volatile memory based devices like flash memory.
As computing capabilities are enhanced in processors, one concern is the speed at which memory may be accessed by a processor. For example, to process data, a processor may need to first fetch data from a memory. After completion of the data processing, the results may need to be stored in the memory. Therefore, the memory access speed can have a direct effect on overall system performance.
Another important consideration is power consumption. For example, in mobile computing devices that rely on battery power, it is very important to reduce power consumption to allow for the device to operate while mobile. Power consumption is also important for non-mobile computing devices as excess power consumption may increase costs (e.g., due to additional power usage, increased cooling requirements, etc.), shorten component life, limit locations at which a device may be used, etc.
Hard disk drives provide a relatively low-cost storage solution and are used in many computing devices to provide non-volatile storage. Disk drives however use a lot of power when compared to flash memory since a disk drive needs to spin its disks at a relatively high speed and move disk heads relative to the spinning disks to read/write data. This physical movement generates heat and increases power consumption. To this end, some higher end mobile devices are migrating towards flash memory devices that are non-volatile.